The present invention relates to a planar display panel which comprises a display panel having a two-dimensional screen to display characters, figures, images, etc. The present invention also relates to a manufacturing method, a controller, and a driving method for the planar display panel.
Hitherto, planar display panels of the type that a plurality of linear electrodes are arrayed in a matrix pattern in opposed relation with a dischargeable gas medium therebetween, and a voltage is applied to selected ones of the electrodes on both sides to develop gas discharge at the intersects of the both-side electrodes, have been disclosed in, e.g., Japanese Unexamined Patent Publication No. 3-160488 and No. 2-90192 and Japanese Unexamined Utility Model Publication No. 3-94751.
Those conventional planar display panels are constructed such that two insulating substrates each being light-transparent are bonded to each other to define a space, electrodes are provided on each of the substrates to form matrix-like discharge electrodes in the space and to position in opposed relation with the space between the electrodes on both sides, and partitions are provided to define a discharge space for each of the electrodes. Then, display control is performed by selecting desired ones of the matrix-like electrodes disposed in opposed relation. It has been therefore impossible to perform display control independently for each of display cells. Also, the above-mentioned structure has necessarily resulted in a large thickness of the planar display panel.
Another conventional planar panel utilizing gas discharge to effect display is described in Ohwaki and Yoshida, xe2x80x9cPlasma Displayxe2x80x9d, November 1983.
This panel is constructed by arranging comb-like electrodes coated with an insulating material, e.g., glass, such that the comb-like electrodes are opposed to each other in a matrix pattern with a discharge space between the electrodes on both sides. Display cells arrayed in units of a row or column are driven together by one comb-like electrode.
Display control of the panel is performed by three operations; i.e., a writing operation in which, of the comb-like electrodes in a row-and-column pattern, the comb-like electrodes on the scan side are driven successively while minute discharge is produced in a display cell locating between the selected comb-like electrode and the electrode opposed to it in the matrix pattern, a sustaining operation for selectively causing only those display cells, in which minute discharge is produced by the writing operation, to emit light over an entire display screen, and a total-writing/total-erasing operation for bringing the display cells into the same electrical condition over the entire display screen.
To display an image, it is required to control luminance for each of the display cells. Because each control and display electrode deals with many display cells at a time and the display cell operates with a binary characteristic (taking only two states of emitting light or not), a special method must be used to achieve gradation display. One driving method is disclosed in, e.g., Japanese Unexamined Patent Publication No. 6-186927.
According to the disclosed driving method, gradation display is achieved by dividing a display period into a plurality of periods having different sustaining periods (or different levels of luminance in sustaining periods) for the purpose of luminance representation, and performing operations of writing and sustaining display data in the respective divided periods, thereby combining the luminance levels in the divided periods with each other.
With the above conventional panel driving method, however, because the opposing matrix electrodes are used for control of display discharge, each electrode must control 100 ore more display cells at a time. Then, display is effected by time sequentially performing a writing step of driving scan electrodes in a group of matrix electrodes one by one, a sustaining step of alternately applying a sustaining voltage pulse to the group of matrix electrodes so that only those display cells, into which display data has been written, emit light for display, and a total-discharging/total-erasing step for making even electrical conditions of the cells effecting display and the cells not effecting display, respectively.
Further, in such a sequence control, the control process necessarily depends on characteristics of the display cells which are susceptible to large individual differences during the manufacturing steps, such as a voltage value to start discharge of each display cell, a minimum voltage value to sustain the discharge, and a writing voltage value for producing writing discharge. The voltage for sustaining the discharge, in particular, often has an allowable range of as narrow as 10 to 20 V because upper and lower limit values of the voltage are determined respectively by the discharge starting voltage and the minimum sustaining voltage.
For the above reasons, control margins for ensuring stable display cannot be set to large values, and the display sustaining voltage, the writing voltage, the discharge starting voltage, etc. need to be adjusted for each display panel. If those voltage values are fluctuated with the continued operation, they must be adjusted again. Another problem is that complicated characteristics of the display cells are subject to large fluctuations even in one sheet of display panel, and hence a production yield is reduced.
Further, in the above-described gradation control method for the conventional gas discharge panel, at least two operations of writing data and sustaining display need to be performed in the number of combinations enough to achieve gradation representation, and the writing operation takes at least 1 to 2 msec. Accordingly, the display sustaining period is discontinuous with the writing periods interleaved therein.
For the gradation representation, control is performed to finish in one sequence (about 16 ms: frame frequency 60 Hz). However, because luminance control cannot be performed continuously in point of time within one sequence, there occurs a mismatch between the gradation representation of display (gradation representation resulted from driving the panel as per design) and perception of luminance change by the human eyes. This raises a problem that discontinuous points in gradation, i.e., the so-called pseudo-contour, is perceived and quality of image display is greatly deteriorated.
The present invention has been accomplished in view of the state of art set forth above, and its object is to provide a planar display panel in which display cells of a display panel can be driven individually on the cell-by-cell basis, and a discharge space has a structure capable of reducing a thickness of the planar display panel, as well as a method for manufacturing the planar display panel.
Another object is to provide a controller for a planar display panel, with which switching control is performed for each of individual electrodes provided independently of one another in one-to-one relation to display cells of a planar display panel, in which the display cells can be individually driven on the cell-by-cell basis, thereby achieving gradation control.
Still another object is to provide a method for driving a planar display panel, which can perform control of sustaining discharge for a display panel having an electrode structure and a panel structure, which enable display cells to be driven individually on the cell-by-cell basis, regardless of discharge characteristics of the individual display cells, particularly a difference between a discharge starting voltage and a minimum discharge sustaining voltage, thereby providing a sufficiently large margin for discharge control, and which inserts an operation for stabilizing discharge at intervals of a predetermined period, thereby sustaining more stable discharge.
Still another object is to provide a method for driving a planar display panel, which performs discharge control in a continuous time range within one sequence, enabling display luminance to be represented in one continuous period, and hence can achieve gradation display suitable for image display.
A planar display panel according to the present invention comprises a first transparent substrate, a pair of electrodes provided on the first transparent substrate, and a second substrate having a recess formed in an area opposing to the pair of electrodes to define a discharge cell of a display cell. Therefore, a planar display panel is provided in which the display cells constituting the display panel can be driven individually on the cell-by-cell basis, and the discharge space has a structure capable of reducing the thickness of the planar panel.
Also, the pair of electrodes provided on the first transparent substrate is arrayed in plural number on the first transparent substrate in juxtaposed relation to form a group of electrodes. Therefore, an electrode pattern for the plurality of discharge cells can be formed with ease.
Further, the recess is rectangular in shape and has a desired depth. Therefore, the discharge space can be directly formed in the second substrate regardless of formation of the electrodes with no need of the barrier to demarcate the discharge space. The thickness of the planar display panel can be hence reduced.
The recess has a depth in the range of 300-600 xcexcm. Therefore, the thickness of the discharge space is increased to provide higher luminance.
A dielectric layer is formed on the first transparent substrate to cover the pairs of electrodes provided. Therefore, electric charges are avoided from diffusing to the outside and can be enclosed in the discharge cells.
A fluorescent material layer is coated on a surface of the recess formed in the second substrate. Therefore, color display can be easily achieved with uniform luminance and hence uniformity of an image.
A reflecting layer is interposed between the bottom surface of the recess formed in the second substrate and the fluorescent material layer. Therefore, light emitted from the fluorescent material layer can be forced to exit forward efficiently.
The pair of electrodes comprise a common electrode provided on the first transparent substrate for driving all of display cells together, which constitute the display screen, or for partly driving any plural number of the display cells at a time, and one of individual electrodes provided on the first transparent substrate for individually driving the display cells on the cell-by-cell basis which constitute the display screen. Therefore, a planar display cell can be provided which has an electrode structure capable of individually driving the display cells of the display panel on the cell-by-cell basis and reducing the thickness of the planar panel.
The depth of the recess formed in the second substrate is set to be three or more times the gap formed between the common electrode and the individual electrode for each display cell to produce discharge. Therefore, the thickness of the discharge space is increased to provide higher luminance.
Evacuation grooves are formed to interconnect the display cells formed in the second substrate and an evacuation through hole is bored in the second substrate to be communicated with the evacuation grooves. Therefore, passages for purging impurity gas through them during evacuation to create a vacuum can be ensured.
Lead pins are vertically provided on the common electrode and the individual electrodes in positions on the first transparent substrate corresponding to between the display cells which constitute the display screen, and electrode leading-out through holes for leading out the lead pins to the back side of the display screen are bored in the second substrate in positions opposing to the lead pins. Therefore, the electrodes can be easily led out to the back side of the display screen.
The lead pins are fused to the bus electrodes of the individual electrodes and the common electrode by a paste or bonding material which is comprised primarily of the same metallic material as that of the bus electrodes of the individual electrodes and the common electrode. Therefore, the lead pins can be firmly fixed to the electrodes.
The lead pins each have a large-diameter base end portion which is fused to the electrode, and the electrode leading-out through holes each have a stepped shape comprising a large-diameter portion in which the base end portion of the lead pin is inserted, and a small-diameter portion through which a distal end portion of the lead pin is extended. It is therefore possible to properly position the lead pin with ease and to prevent a useless gap from being caused between the first and second glass substrates.
A sealing guard is provided near a portion where the lead pins are fused, so that a sealing material is prevented from flowing into the display cells when an assembly of the first and second glass substrates is sealed off. Therefore, a sealing material can be surely prevented from flowing into the display cells.
Further, a method for manufacturing a planar display panel according to the present invention comprises the steps of patterning transparent electrodes of the individual electrodes on the first transparent substrate, forming the bus electrodes of the individual electrodes and the common electrode on the first transparent substrate with the transparent electrodes formed thereon, forming a dielectric layer to cover the individual electrodes and the common electrode on the first transparent substrate, vertically fixing the lead pins to the individual electrodes and the common electrode through the electrode leading-out windows formed in the dielectric layer, forming a protective film on the first transparent substrate having been subjected to the pin fixing step, forming, in the second substrate, the recesses for defining the discharge spaces of the display cells which constitute the display screen, the electrode leading-out through holes for leading out the lead pins, which are vertically fixed to the common electrode and the individual electrodes, to the back side of the display screen, and the evacuation through hole, forming the fluorescent material layers on the bottom surfaces of the recesses defining the display cells, fitting the first and second substrates fabricated through the above steps to assemble a panel such that the lead pins on the first transparent substrate are extended to the outside via the through holes of the second substrate, and sealing the assembled panel of the first and second substrates. It is therefore possible to easily manufacture a planar display panel which has an electrode structure capable of individually driving the display cells of the display panel on the cell-by-cell basis and reducing the thickness of the planar panel.
Moreover, according to the present invention, in a controller for a planar display panel comprising a common electrode for driving all of display cells together, which constitute a display screen, or for partly driving any plural number of the display cells at a time, and individual electrodes for individually driving the display cells on the cell-by-cell basis, the controller includes a driving circuit for changing luminance in accordance with the number of pulses applied to each of the individual electrodes within a unit time, thereby effecting gradation display. It is therefore possible to achieve gradation control with switching control performed for each of the individual electrodes provided independently of one another in one-to-one relation to the display cells.
The driving circuit effects the gradation display based on control of application of a relatively wide sustaining pulse and a relatively narrow extinguishing pulse which are used as the pulses to be applied to each of the individual electrodes within the unit time. Therefore, discharge display can be stopped during a period in which the extinguishing pulse is applied, and hence the gradation display can be achieved as desired.
In addition, the planar display panel is constituted by display modules as constituent elements each comprising a plurality of display units combined into a pattern of row-and-column matrix, the display modules arranged in the horizontal direction are cascaded, and a power supply is connected to the display modules in parallel. A signal processing circuit for applying control signals to the driving circuits of each of the display modules comprises an address information storage unit for storing specific address information, an input signal control unit for allowing input data to pass through it and taking data, which the display module including that control unit is to represent by itself, out of a position indicated by the specific address and a display effective signal in the data, a through data output buffer for outputting the data, which has passed through the input signal control unit, to the adjacent display module cascaded downstream, a memory into which the data taken out of the input signal control unit is written in response to a write control signal, and from which the data is read in response to a read control signal, a display pulse generator for generating common electrode and individual electrode driving pulses based on the data taken out of the input signal control unit, a counter for counting the common electrode driving pulse output from the display pulse generator, a look-up table for converting the number of pulses counted by the counter into a numerical value of gradation data, a display data generator for outputting individual electrode control data based on comparison between the gradation data from the look-up table and the individual electrode driving display data read from the memory, and an output buffer for outputting signals of the display pulse generator and the display data generator to the individual electrode driving circuits and the common electrode driving circuits. Therefore, when data control is performed for the plurality of display modules combined with each other, individual control of the respective display modules in accordance with the display data can be achieved by taking in the display data corresponding to the address of each display module.
Furthermore, according to the present invention, in a method for driving a planar display panel in which a pair of a common electrode driven in common and an individual electrodes driven individually are provided side by side for each of a plurality of cells, and a voltage pulse is applied to the common electrode to produce luminescence due to discharge on a dielectric layer formed over the common electrode and the individual electrode, the method comprises the steps of applying a voltage pulse to the individual electrode to reverse the polarity of wall charges accumulated on the dielectric layer, and then applying a voltage pulse to the common electrode so that an electric field of the wall charges caused upon the reversal of the polarity is additionally applied. With this feature, discharge produced by applying one composite voltage pulse to the common electrode functions to not only start the discharge, but also initialize the display cell with erase discharge, and therefore a large control margin can be set for the display operation. Further, by applying display initializing pulses to all the individual electrodes at constant intervals, even when discharge produced upon driving of the common electrode becomes unstable, display can be maintained in a stable state, thus resulting in very stable display.
Also, assuming that one sequence is defined by a certain number of voltage pulses applied to the common electrode, the voltage pulse is applied to the individual electrode in units of one or plural sequences.
The voltage pulse applied to the common electrode functions to start discharge at rising of the voltage pulse as a result of addition of the electric field of the wall charges caused upon the reversal of the polarity, and to produce erase discharge at falling of the voltage pulse with wall charges caused by the started discharge.
The voltage pulse applied to the common electrode is a composite voltage pulse comprising a first voltage pulse not higher than the discharge starting voltage and a second voltage pulse superposed within a period of the first voltage pulse, the composite voltage pulse having a voltage value not less than the discharge starting voltage.
Erase discharge is produced due to the wall charges at falling of the first voltage pulse.
The method for driving a planar display panel may further comprise the step of applying the voltage pulse to the individual electrode to stop the discharge after erase discharge has been produced by the composite voltage pulse applied to the common electrode.
When the voltage pulse is applied to the common electrode to produce discharge, a voltage in a discharge sustaining region is applied to the individual electrode of the display cell in which the discharge is to be sustained, and a voltage in a discharge suppression region is applied to the individual electrode of the display cell in which the discharge is to be stopped. With this feature, the common electrode has a function of sustaining discharge, all the display cells can be driven at a time, and display control can be performed by driving the individual electrodes at a lower frequency. Therefore, the circuit configuration is simplified. In other words, circuits requiring large power can be concentrated on a section for driving the common electrode, while the individual electrodes can be driven by circuits operating at a lower voltage and consuming less power. As a result, an inexpensive and highly-reliable planar display panel can be manufactured.
Assuming that one sequence is defined by a certain number of voltage pulses applied to the common electrode, gradation display is made by applying a voltage in a discharge sustaining region enough to sustain the discharge to the individual electrode corresponding to the number of voltage pulses in one part of one sequence, thereby providing a display sustaining period, and by applying a voltage in a discharge suppression region to stop the discharge to the individual electrode corresponding to the number of voltage pulses in the other part of one sequence, thereby providing a display suppression period. With this feature, gradation display is realized by setting a continuous display period in one sequence, whereby gradation display having high quality and suitable for image representation can be achieved.
The front half of one sequence provides the display sustaining period and the second half of one sequence provides the display suppression period.
The certain number of voltage pulses applied to the common electrode within one sequence is selected to be not less than the number of gradation steps, and a plural number of voltage pulses are assigned to one gradation step.